The invention relates to a method for interlocking plastic bags in stacks, particularly bags for automated machines, through fusion.
In the plastic bags of the discussed kind, particularly bags for automated machines, it is known that during manufacturing the bags are provided with suspension or stacking openings, in order to enable them to be deposited in packages, immediately after production, on the stacking pins of a stacking chain, thereby forming a stack of bags. When a sufficient number of bags have been stacked on each pair of stacking pins, the respective pair of stacking pins is moved further, so that on the next pair of stacking pins of the driven revolving stacking pin chain, stacks of bags can again be formed. In order to insure that in each stack the individual plastic bags can be kept together, an interlocking is performed directly on the stacking pin chain. For the interlocking an interlocking station is required. The latter is not only expensive, but also requires a large amount of space, so that the stacking pin chain is relatively long. Bag stacks of the mentioned kind are known from the German Utility Model 74 29 628. For the interlocking of the bag stacks so-called glow plugs or glow pegs, which after being intensely heated are pushed through the stack of bags. optionally an opening can be stamped prior to that at the punch-through location. The interlocking of the plastic bags in the bag stack takes place directly downstream of the actual stacking process, i.e. within the area of the pin stacking conveyor. At the end of the pin stacking conveyor the interlocked bag stack is removed by an operator, optionally again examined for quality control and finally delivered to a transport station.
In the case of bag stacks which are not interlocked by fusion but are interconnected by the insertion of a wire bracket with additional safety plates or rubber stoppers, due to the numerous steps required for the formation of a bag stack, it has also become known to replace the manual handling by a robot, as described and represented in detail in EP 0 384 281 A1.
It is the object of the invention to provide a low-cost method of the kind mentioned in the introduction, through which the stacking of bags into a block (stack or pad) and the securing of the stacked bags by fusion is further simplified.
In order to achieve this object, in a method of the kind discussed at the outset, the interlocking of the plastic bags in the stack is effected through fusion after the bag stack is seized and clamped by a grip hand of the robot, by means of an interlocking device. According to the invention the bag stack is held on a pair of stacking pins and is seized by clamping by the robot grip hand and subjected to fusion immediately thereafter. At very high production speeds, the interlocking of the bag stack can even take place during the transport of the bag stack to a transfer station by the robot. This means that no additional time is required for the interlocking; moreover the transport time which is anyway needed by the robot between the pickup of the bag stacks from the pin stacking conveyor and the transfer to the delivery station is used for interlocking.
In the new system the interlocking device for the housing and the clamping mechanism are eliminated. Besides the stations freely suspended stations provided in the pin stacking chain for interlocking purposes can be used for manual or automated correction and supervision functions.
If necessary, the interlocked bag stacks can be suspended via stacking holes in the transfer station, for intermediate storage. In this way the interlocking locations have enough time to cool down, so that the bag stacks interlocked according to the invention can be packed into cardboard boxes relatively quick.
According to the invention a suitable device for the stackwise interlocking of plastic bags, particularly bags for automated machines, through fusion by means of an interlocking device is designed so that the interlocking device is integrated in a grip hand of the robot which picks up the bag stack from a stack-forming device and transfers it to a delivery station. In this way the grip hand of the robot takes over not only transport tasks, but at the same time performs the stack formation, whereby an essentially disturbance-free handling of the bag stack from its pickup from the pin stacking conveyor up to the transfer to the delivery station results.
In a suitable embodiment of the invention, the interlocking device is fastened to a mounting plate of the grip hand, namely ideally on a cross-section preferably having T-shaped grooves, which is adjustably supported on the mounting plate. In this way an adjustment to the respective format of the plastic bags is possible. For the fusion itself, it is sufficient to provide a heat source, for instance two glow plugs arranged at a distance from each other and a cylinder-piston unit, for instance in the form of a pneumatic cylinder, for their adjustment.
It has proven to be particularly suitable when the glow plugs are arranged respectively in the area of a first clamping bar of the grip hand, which is adjustable with respect to the second clamping bar of the grip hand, as well as to the glow plugs.
Optimal conditions for the clamping and the interlocking result when both glow plugs are arranged outside the clamping locations of the clamping bars of the grip hand.
In this way it is relatively simple to design the upper clamping bar as a wiper for the interlocked bag stack, when for instance the clamping bar is provided with a passage opening for the respectively arranged glow plugs.